The aim here is to produce tidal current data in the form of grib files that will work with OpenCPN.
CDO can be used to convert Copernicus netCDF (.nc) files to tidal current gribs for display using OpenCPN.
Downloading Copernicus netCDF (.nc) files requires registration with the CMEMS service of Copernicus. Apply here: Registration
The CDO program is an extensive suite of tools. Only a minute fraction of it's power is being used here.